What is gas insulated substation?

 

1. What is Gas insulated Substation?

 

         

         A Gas insulated substation (GIS) is a high voltage substation in which the major structures are contained in a sealed environment with sulfur hexafluoride gas as the insulating medium. GIS technology originated in Japan, where there was a substantial need to develop technology to make substations as compact as possible. The clearance required for the phase to phase and phase to ground for all equipment is much lower than that needed for an air-insulated substation. The total space required for a GIS is 10% of that required for a conventional substation.

       Gas-insulated substations offer other advantages in addition to the reduced space requirements. Because the Substation is enclosed in a building, a GIS is less sensitive to pollution, as well as salt, sand, or large amounts of snow. Although the initial cost of building a GIS is higher than making an air-insulated substation, the operation and maintenance costs of a GIS is less.

 

 

2. Specifications of GIS

 

         The metal-enclosed gas-insulated switchgear, including the operating devices, accessories, and auxiliary equipment forming an integral part thereof, shall be designed, manufactured, assembled, and tested following the following International Electro-technical Commission (IEC) standards.

• IEC 62271-203 – Gas Insulated metal-enclosed switchgear for rated voltages above 52KV.

• IEC 62271- 100 – High voltage alternating current Circuit breakers.

• IEC 60694 – Common clauses for high voltage Switchgear and control-gear standards.

• IEC 62271-102 – Alternating current disconnectors (isolators) and earthing switches.

• IEC 61128 – Alternating current disconnectors. Bus-transfer current switching by disconnectors.

• IEC 61129 – Alternating current earthing switches.

• IEC 66044-1 – Current transformers.

• IEC 66044-2 – Voltage transformers.

• IEC 60137 – Bushings for alternating voltages above 1000 V.

• IEC 60859 – Cable connections for gas-insulated switchgear.

• IEC 60480 – Guide to checking of sulfur hexafluoride taken from electrical equipment.

• IEC 60099-1/4 – Non-linear resistor type arresters for AC systems.

• IEC 60439 – Factory-built assemblies of low-voltage switchgear and control gear.

• IEEE 80 (2000) – IEEE Guide for Safety in AC Substation Grounding.

 

 

3. Advantages of GIS and Hybrid system

 

 

 GIS is an advanced technology, needs lesser space (35%), lower maintenance costs, and outages compared to AIS.

 The initial cost of GIS is higher by about 50% than AIS, but when the value of land is considered in capital cost, the overall capital cost is comparable.

 Wherever land is a constraint, GIS is the best option.

 Hybrid Technology, which is a mix of AIS & GIS, combines the benefits of both AIS and GIS (Initial capital cost 20% higher than AIS).

 Hybrid technology requires moderate land size (50% of AIS and 50% higher than GIS).

 Flexibility in terms of future expansion in Hybrid technology is high (similar to AIS).

 

4. Applications of GIS and Cost of ownership

 

Application:-

• High voltage installations The higher the voltage, the more promising Gas-insulated technology becomes. The footprint of a 765kV conventional Substation is enormous, and GIS technology allows a significant size reduction.

• Urban Installations GIS technology can be used for installations in areas where the cost of real estate or aesthetic appeal is a significant consideration. Indoor Installations Building an air-insulated substation indoors is usually impractical, but a GIS can quickly go inside buildings.

• Environmentally Sensitive Installations GIS technology is prevalent in desert and arctic areas because it can be enclosed in a building with environmental control. Gas-insulated substations also contain the electrical components within a Faraday cage and are therefore totally shielded from lightning.

Total Cost of Ownership:-

    On a high-level comparison of AIS and GIS switchgear, you need to weigh the upfront costs against the required lifelong maintenance. These units generally have a 30-year minimum life span. GIS units tend to cost between 10% to 40% more than AIS.

    AIS systems offer upfront cost savings. However, they require more person-hours over the long run. GIS high voltage substations advanced electrical engineering requires a more massive upfront investment, but their sealed technology leads to lower installation and maintenance costs.

 

5. Comparison of AIS and GIS